1. Field of the Invention
The present invention relates to an electronic throttle control apparatus for controlling an opening degree of a throttle valve by driving, through an electric motor, the throttle valve located in an air inlet passage of an internal combustion engine of a vehicle.
2. Description of Related Art
There is known, as disclosed in Japanese Patent Application Laid-open No. 2000-320348, a throttle control apparatus having a configuration in which a target opening degree of a throttle valve is oscillated within a certain angular range that does not affect starting characteristic of an engine during its starting period before the engine begins complete explosion, if there is a possibility that ice pieces have been formed in the throttle valve.
Since an output torque of a vehicle engine during its starting period does not vary so much even when a throttle valve is oscillated widely, it becomes possible to remove ice pieces from the throttle valve by oscillating the throttle valve.
However, in a case where the ice pieces formed in the throttle valve stick to an inner surface of an air inlet pipe at a binding force larger than a throttle valve driving force of an electric motor, there is a possibility that the throttle valve cannot recover from the frozen state thereof, that is, the ice pieces cannot be removed from the throttle valve even if the target opening degree of the throttle valve is oscillated during the engine starting period.